The problem is that no warrant is needed if the phone company complies without asking for one.
Basically the government says "hey can we see this users data? (And if you say no, we'll get a warrant that requires you to do extra work)", and then the phone company turns over your data without requiring the warrant because they don't care about you.
I was specifically addressing OP's statement that the warrant requirement does not offer much protection - I'm not talking about situations where a warrant is not required. I think I probably agree with you that over-compliance by phone companies is a problem, but that's not what I was asking about.
