kěyǐ yòng kèfúdiànhuà bànlǐ yínhángkǎ guàshī ma?

A very common Chinese pattern is:

modal verb + method/tool + main verb + object + question particle

So here:

• 可以 = can / may / is it possible to
• 用客服电话 = by using the customer service phone line
• 办理 = handle / process
• 银行卡挂失 = reporting a bank card as lost
• 吗 = turns the sentence into a yes-no question

So the structure is very natural in Mandarin: Can [someone] use the customer service phone line to handle a bank card loss report?

Here, 可以 means can, may, or is it possible to.

It does not only mean permission. In this sentence, it mainly asks about possibility or available method:

• 可以吗？ = Is it possible?
• 可以用客服电话办理……吗？ = Is it possible to do this through the customer service phone line?

So it is similar to English Can you do this...?

Chinese often omits the subject when it is obvious from context.

So although English usually wants a subject, Mandarin does not always need one. Depending on the situation, this sentence could imply:

• 我可以用客服电话办理银行卡挂失吗？
  = Can I use the customer service phone line to report my bank card lost?
• 可以用客服电话办理银行卡挂失吗？
  = Can one do this by calling customer service?

Both are natural. The shorter version is very common.

用 literally means to use, but in this sentence it means by using / through / via.

So:

• 用客服电话 = using the customer service phone line
• more naturally in English: through the customer service phone line

This is a very common use of 用 in Chinese:

• 用手机付款 = pay using a phone
• 用微信联系我 = contact me through WeChat

Both are understandable, but they feel slightly different:

• 用客服电话 = using the customer service phone line
  
  • common and conversational
• 通过客服电话 = through the customer service phone line
  
  • a bit more formal or explicit

So:

• 可以用客服电话办理银行卡挂失吗？ = natural
• 可以通过客服电话办理银行卡挂失吗？ = also natural, slightly more formal

客服电话 means customer service phone number / customer service hotline / customer service line.

It breaks down like this:

• 客服 = customer service
• 电话 = telephone / phone

Together, 客服电话 is a set phrase meaning the phone line you call for customer service help.

Because Chinese often makes compound nouns by putting nouns directly together, without 的.

So:

• 客服 + 电话 → 客服电话
• literally: customer-service phone

Using 的 here would sound less natural in this fixed expression. Many everyday Chinese nouns work like this:

• 银行卡 = bank card
• 手机号 = mobile phone number
• 服务中心 = service center

办理 means to handle, to process, or to go through the formal procedure for something.

It is often used for official or administrative matters, such as:

• 办理签证 = apply for / process a visa
• 办理手续 = complete formalities
• 办理业务 = handle business/services

In this sentence, reporting a lost bank card is treated as a formal banking service, so 办理 is very appropriate.

挂失 is a fixed term meaning to report something as lost, especially important items such as:

• bank cards
• ID cards
• passports
• phones
• account credentials

So if your bank card is missing, 挂失 means you officially notify the bank so the card can be blocked or protected.

This is more specific than just 丢了 (lost).

• 银行卡丢了 = the bank card is lost / missing
• 银行卡挂失 = reporting the bank card lost to the bank

It is better thought of as a phrase or service item, not a single simple word.

Breakdown:

• 银行卡 = bank card
• 挂失 = report as lost

Together:

• 银行卡挂失 = bank card loss reporting / reporting a bank card as lost

After 办理, this whole chunk acts as the object:

• 办理银行卡挂失 = handle the procedure of reporting a bank card lost

Yes. 挂失 can be used directly as a verb.

For example:

• 我要挂失银行卡。
  = I need to report my bank card as lost.
• 这张卡已经挂失了。
  = This card has already been reported lost.

In your sentence, though, it appears inside the more formal expression:

• 办理银行卡挂失

That sounds like discussing the service or procedure itself.

You certainly can say 打客服电话, but it shifts the focus slightly.

• 打客服电话 = call the customer service phone line
• 用客服电话 = use the customer service phone line as the method/channel

Compare:

• 可以打客服电话办理银行卡挂失吗？
  = Can I call customer service to report the card lost?
• 可以用客服电话办理银行卡挂失吗？
  = Can this be handled through the customer service phone line?

Both are natural. The original sentence emphasizes the channel or means, not just the physical act of making a call.

吗 turns the sentence into a yes-no question.

Without 吗, the sentence is a statement:

• 可以用客服电话办理银行卡挂失。
  = It is possible to handle a bank card loss report through the customer service line.

With 吗:

• 可以用客服电话办理银行卡挂失吗？
  = Can it be handled through the customer service line?

This is one of the most basic and important Mandarin question patterns.

Some natural answers are:

• 可以。
  = Yes, you can.
• 可以办理。
  = Yes, it can be handled.
• 可以，用客服电话就能办理。
  = Yes, you can handle it through the customer service line.

Negative answers:

• 不可以。
  = No, you can’t.
• 不行，需要去银行柜台。
  = No, you need to go to the bank counter.
• 客服电话不能办理挂失。
  = The customer service line cannot handle loss reporting.

It is fairly neutral, with a slightly service-related / practical tone because of words like 办理 and 挂失.

It sounds natural in situations like:

• asking bank staff
• asking customer service
• asking someone how to handle a lost card
• checking whether a service is available by phone

It is not slangy, and it is not overly formal either. It is very useful real-world Mandarin.