Personally I'm quite okay with Windows 10. A bit slower than 8, but feels generally like an okay upgrade.
My biggest gripe with it is the upgrade method. Nice they're backing away, but considering it's about a month till free upgrades stop being a thing, it seems rather disingenuous, like they're only backing off now to make sure people who managed to remain on 7 and 8 wouldn't be missing an update removing the offer after it expired and incoming complaints about false advertising.
I work IT support for a school. During exams this summer we've had 4 students whose computer decided to upgrade DURING an exam. 3 of them about 5 minutes after a written exam started, one when reading notes while preparing for an oral exam.
My take away is: Windows 10 is a nice OS. This, and the "ready or not, we're updating now" updates of Win 10 means if were to have a computer used for anything mission critical which must not suffer downtime, I'd advise caution against WIndows. I can follow their thinking, people on 8 and especially 7 and older would ignore critical security updates for months at a time, then complain when they got hit by an exploit long patched.
Altogether removing the option to delay further than 24 hours is...stupid. In my opinion they should've carried on with the Windows Vista/7 way of having an annoying popup tell you to update your system and let you postpone it maybe 24 hours first off, when next it shows up, cut it to 12 hours, then 6 hours down to 1 hour. Pester people to apply patches (let super users set further delays through a commandline, if it's so mission critical it cannot be rebooted there's bound to be at least one tech-savvy person reachable).
As to the Mobile phone pestering, I believe that's a feature of a Live account, not Windows 10. But if you sign in with a Live account, it will likely pester you to add a phone number for two factor protection of your account. Got that done with my Live account some time ago, only messages I've gotten on it has been "A new device wants to access your Live account, if you initiated this, enter this pin code"