Steam keeps asking to add my telephone number :/

Don't do it. Steam will act all glad at first, but then when real life needs attention Steam will start calling you, asking why it never hears from you anymore, if you are still in love, or are you having second thoughts about the relationship. If you continue to ignore it, it'll find your work number and leave embarrassing messages with the front desk, accuse you of cheating on the relationship with GOG or Desura. You'll try to point out that even if you had had something with Desura in the past, it can't possibly be a thing anymore. Steam won't be satisfied and will continue to stalk you until you play all the time as proof of your devotion.

Don't hand over your number, really it's for the best.

It keeps asking my number too even though I already added it.

Just wanted to reply "No, I've never had it asking me."

Then I checked my steam, and what do I see? Yes, it's probably a bug, because they already have mine

Steam Client Beta Update - September 16th

We've just updated the beta once again:

Edit: this update was re-released with additional changes at 4:50pm PST

General
• Fixed bug causing category info to be missing from the Library in Offline Mode, and sometimes cleared permanently when going back online
• Fixed phone reminder bar always showing on startup
• Added a separate library category for SteamVR-enabled games

In-Home Streaming
• Fixed a recent bug which could cause input packets to be dropped

VR Mode
• VR mode now automatically launches the VR mode of apps if there is one configured.

its gone, at least for me... restart steam