Learn Hardcore Portuguese (Brazil): A tela do meu celular foi consertada, mas o botão ainda está estranho. - My phone’s screen was fixed, but the button is still strange.

Because tela is feminine (a tela), but the thing it belongs to is o celular (masculine).
So you get: a tela + de + o meu celular = a tela do meu celular.
If the owner noun were feminine, you’d use da (e.g., a tela da minha TV).

What’s the role of foi consertada? Why not just é consertada or consertaram?

foi consertada is passive voice in the past: was fixed/was repaired. Structure: ser + past participle.

A tela foi consertada = the screen got repaired (focus on the screen, not who did it).
A tela é consertada would normally mean “is repaired” in a general/habitual sense (or can sound like a description, not a completed event).
Consertaram a tela = “They fixed the screen” (active voice; subject is unspecified “they”).
Portuguese often uses both; passive (foi consertada) is common in more formal or neutral statements.

Why is consertada ending in -a?

Because the past participle agrees with the noun it describes in passive voice: a tela is feminine singular, so consertada (fem. sing.).
Compare:

O celular foi consertado (masc. sing.)
As telas foram consertadas (fem. plural)
Os celulares foram consertados (masc. plural)

Is consertar the most natural verb here? What about arrumar or reparar?

All can work, but they have slightly different feel:

consertar = very common for fixing devices; straightforward and natural.
reparar = also “to repair,” often a bit more formal/technical.
arrumar = “to fix” in a broader sense (tidy up / sort out / fix). For electronics, arrumar is common in speech but slightly less specific than consertar.

What does mas do, and could I use porém or só que?

mas = “but,” standard contrast connector.
Alternatives:

porém = “however,” a bit more formal.
só que = “but (the thing is…),” very common in conversation and can feel more emphatic.
Your sentence works with any of them, with a shift in tone:
... foi consertada, mas/porém/só que o botão...

Why is it o botão and not um botão?

o botão refers to a specific button that both speaker and listener can identify (often “the button on the phone,” or a known problematic button).
um botão would sound like “a (certain) button” or one of several buttons—less specific.

What’s the function of ainda in ainda está estranho?

ainda means “still / yet,” indicating the situation continues despite the repair.
So: the screen was fixed, but the button is still weird.
Without ainda, it would just state the current condition: ... but the button is weird.

Why use está instead of é with estranho?

In Portuguese, estar often describes a temporary or changeable state, while ser describes a more inherent/characteristic trait.
Here, the button being weird is treated as a current condition (maybe due to the repair), so está estranho fits well.
é estranho could sound like “it’s strange (in general/by nature)” or a more permanent judgment, though in some contexts people do say it.

Does estranho mean “strange,” “weird,” or “broken”?

Here estranho usually means “weird / not right / acting odd.” It doesn’t necessarily mean fully broken, just abnormal.
If you want clearly “broken,” you might say:

ainda está com defeito = it’s still defective
ainda não funciona direito = it still doesn’t work properly
ainda está quebrado = it’s still broken

Why not say o botão ainda está esquisito? Is there a difference between estranho and esquisito?

Both can mean “weird,” but:

estranho is very common and neutral; also used for “odd/unusual.”
esquisito can feel a bit more colloquial and sometimes stronger (“creepy/uncanny” in certain contexts).
For a malfunctioning button, estranho is very natural; esquisito is possible too.

Could I replace foi consertada with está consertada?

You can, but the meaning shifts:

foi consertada = emphasizes the completed action in the past (“was repaired”).
está consertada = emphasizes the resulting state now (“is repaired/it’s fixed now”).
In your full sentence, foi consertada contrasts nicely with mas... ainda..., implying “they repaired it, but the problem persists.”

Why is there a comma before mas?

In Portuguese, it’s standard to put a comma before mas when it joins two independent clauses (each with its own verb):

A tela ... foi consertada, mas o botão ... está estranho.
In very short sentences you might see it omitted informally, but the comma is the norm in writing.

Can I say A tela do meu celular consertou?

Not really. consertar is typically transitive: someone fixes something.
To avoid mentioning who, you’d usually use:

passive: A tela ... foi consertada
or impersonal/unspecified subject: Consertaram a tela...
Some verbs can be used like “it fixed itself,” but consertar usually isn’t used that way for screens.

Is celular the best word for “cell phone” in Brazil? What about telefone or smartphone?

In Brazil, celular is the everyday word for mobile phone.

telefone is broader (“telephone”) and can sound less specific.
smartphone is also used, especially when contrasting with simpler phones, but celular is the default in most contexts.

Could I omit meu and just say A tela do celular?

Yes. A tela do celular means “the phone’s screen” in a general way or when ownership is obvious from context.
Adding meu makes it explicit: my phone’s screen.

What’s the difference between botão and tecla here?

botão = a button (often something you press/click; could be physical or on-screen depending on context).
tecla = a key (like a keyboard key) or a physical key/button, often used for specific keys (volume keys, keyboard keys).
For a phone, both can appear depending on what you mean: botão de ligar (power button) is very common; tecla can also be used, but botão is often the default.

How would I talk about which button is weird (power button, volume button, home button)?

You can specify with de + function:

o botão de ligar / botão de energia = power button
o botão de volume = volume button
o botão home (less common now, but used)
Example: ... mas o botão de ligar ainda está estranho.