This field should be Required and its name not editable.This field is still listed as "Optional" on the Manage Forms screen (v1.10.4). As it has always been optional I had renamed it to "office" a long time ago and created a second entry "mobile". Every time I've tried to upgrade in the past year it hasn't worked and I've reverted. I finally got sick of this and dug into it. Turns out that the user search functionality (ie in the new ticket screen at the very least) now automatically searches by phone number. It's none too pleased when that field doesn't exist (or in my case has a different name).Any fields that are hard-coded like this should be locked down... as much as I like the ability to customize things.