does steam need a phone number?

[sparelaptopemail]

does steam need a phone number for sign up and to buy games with a gift card?

[wuddih]

to answer your question:
no for signup
no for purchases (the billing information used to have a required phone number field, it should no longer have it)

for what is the phone number used?

Having a phone number associated with your account will help you recover your account if it is compromised, or if you've lost your password, access to your email account, or your Steam Guard mobile authenticator.

it is used to setup mobile authenticator
and in some games a phone number has to be associated with your account to gain some form of special status to do more things in the game. f.e. playing ranked in dota