I have seen 2 phrases for asking someone what they want to drink.
ne icersiniz? and ne icmek istersiniz? can they both be used?

Does ne istersiniz? mean what would you like? does this refer to anything such as food, drink, choosing something in a shop..

how do you say ...what is your telephone number?

Selam

ne icersiniz ?>>>>>> >>>>> what do you drink ?
ne icmek istersiniz ?>>>>>> what do you want to drink ?

Both of them are only for drinks

ne istersiniz ?>>>>>>>>> what do you want ?

This can be used for everything ( not only food or drink). And another pharese that you can hear in restaurants is

ne arzu ederdiniz ? >>>>>>> what do you want? ( for everything again)

what is your telephone number ?>> telefon numaranız nedir?

İyi günler

cok tesekkurler.

iyi gunler