Me molesta cuando alguien mira el móvil en la videollamada.

Because molestar often works like gustar.

In Me molesta cuando alguien mira el móvil en la videollamada, me means to me, and molesta means is annoying or bothers. So the structure is literally:

To me, it is annoying when someone looks at their phone during the video call.

The annoying thing is not me. The annoying thing is the whole situation.

If you wanted a structure closer to English I am annoyed, you could say Estoy molesto if you are male or Estoy molesta if you are female, but that is a different way of expressing the idea.

It is singular because Spanish treats the whole situation as one thing.

The idea cuando alguien mira el móvil en la videollamada is understood as a single event or circumstance that bothers you, so molesta stays in the third-person singular.

Compare:

Me molesta llegar tarde = Being late bothers me
Me molestan los retrasos = Delays bother me

In the second example, los retrasos is clearly plural, so the verb becomes molestan.

Because here cuando refers to something that happens in general or repeatedly, not to a future or hypothetical event.

So Spanish uses the indicative:

Me molesta cuando alguien mira el móvil
= It bothers me when someone looks at their phone

This means something like whenever that happens or in those situations.

You usually get the subjunctive after cuando when the action is in the future or not yet known to be real:

Me molestará cuando alguien mire el móvil
= It will bother me when someone looks at their phone

So:

• cuando + indicative = habitual, repeated, known, real
• cuando + subjunctive = future, expected, not yet realized

Yes, and that is also correct, but the structure is slightly different.

With Me molesta que..., Spanish normally uses the subjunctive after que because molestar expresses an emotional reaction or evaluation.

So:

Me molesta que alguien mire el móvil en la videollamada

is a very natural sentence.

The difference is roughly this:

• Me molesta cuando alguien mira... = It bothers me when that happens
• Me molesta que alguien mire... = It bothers me that someone is looking or might look

The version with cuando feels more like a general repeated situation.
The version with que feels more like you are reacting to the fact itself.

Because alguien is grammatically singular.

Even though alguien means someone and could refer to any person, Spanish treats it as singular, so the verb must also be singular:

alguien mira
not alguien miran

This is the same idea as English someone looks, not someone look.

Mirar and ver are related, but they are not exactly the same.

• mirar = to look at, to direct your eyes toward something
• ver = to see, to watch, to perceive visually

In this sentence, mirar el móvil is natural because the point is that the person is directing their attention to the phone instead of the video call.

Ver el móvil is less natural here, because you are not just talking about seeing it. You are talking about actively looking at it.

So mirar is the better choice.

This is very common in Spanish.

Spanish often uses the definite article where English would use a possessive such as their, his, or her, especially when the context already makes the meaning clear.

So:

mira el móvil

often means:

looks at their phone

not necessarily looks at the specific phone we already mentioned.

If you said su móvil, that would sound more explicit and could be used if you really want to stress whose phone it is.

If you said un móvil, it would sound more like a phone, which is less natural in this situation.

Because this is Spanish from Spain.

In Spain, the usual word is:

móvil

In much of Latin America, people often say:

celular

Both mean mobile phone or cell phone, but móvil is the expected choice in Spain.

Here en means something like in or during the context of the video call.

So en la videollamada means during the video call or on the video call.

Spanish often uses en with activities or situations:

en clase = in class
en la reunión = in the meeting
en la videollamada = in the video call

You could also hear:

durante la videollamada

which is a bit more explicitly during the video call.

And if you want a more general meaning, en una videollamada is also possible:

Me molesta cuando alguien mira el móvil en una videollamada.

That sounds a little more clearly generic.

The accent mark shows where the stress goes.

móvil is stressed on the first syllable:

MÓ-vil

Without the accent mark, Spanish spelling rules would make you expect the stress somewhere else, so the written accent is necessary.

This is one of many cases where accent marks are not optional decoration. They tell you how the word is pronounced.

Yes. That is completely grammatical.

Both versions are natural:

Me molesta cuando alguien mira el móvil en la videollamada.
Cuando alguien mira el móvil en la videollamada, me molesta.

The difference is mostly emphasis.

• Starting with Me molesta puts the focus first on your reaction.
• Starting with Cuando alguien mira... puts the situation first.

The meaning stays essentially the same.