Without proper tools in an environment I can't think in with someone literally breathing down my neck (or on the other side of the phone line). Yeah, I am upset because I can't think in those conditions and neither can most people.

The pressure is a little higher than real life, but the problem is easier. The phone interview questions are things like "write atoi()", not "write a database system to handle 4000 transactions per second per entity group with globally-consistent reads across three continents", which is the kind of work you might be interviewing for.

I think success at a phone interview question is a good positive signal. That's all you can get in interviews, signals.