USB datalink instability caused by other loads on circuit?

Take a look at ground loops.. It has a good explanation, but is geared toward measurement equipment. The phenomenon is the same though. In short, if all the equipment doesn’t have the exact same ground, you should add a ground cable between them. “Same” would be the same outlet on the same breaker. One on outlet, one on power strip on the same outlet, and one on UPS on the power strip on the same outlet, aren’t necessarily the same ground (although they should be).

Also, motors are VERY electrically noisy devices. Combined with the above, you need to be really careful with how things are connected.

Also, in general, anything with an AC motor shouldn’t be run through a UPS.
A surge protector is not necessarily a noise reducer. You should at least have a surge protector (not a “power strip”) and preferably one that specifically says it has a noise filter as well.

For plugging in the phone, it could be coincidental or a REALLY bad/noisy switching power supply in the charger.