Do they require phone number?
For sign ups, yes. Verification only needs for withdrawal purposes.
Unlike in the past where Basic Verification requires only phone number, it's now need documents. And as what I heard just less than a month ago, those who already verified asked to be verified again or their verification status is back to Basic or something like that. I think most exchanges now are removing mobile phone verification as what XAPO did recently.
yes they require phone number. you can bypass this by doing one of those online sms verifications, from a site that lets you receive sms online for free ...
If for long term account, this is not recommended.