If a drug patent hasn't passed phase 3 trials isn't it just an idea?

Clinical trials and regulatory approval are independent of the patent process. This should make sense because a patent is a right to exclude others, not a right to do something. For example, just because you have a patent on a new drug doesn't mean you can actually sell it to patients.

You don't have to have a physically working thing to patent it. You can patent something that's just an "idea" as long as the idea is physically realizable. Ideally the patent examiner knows enough about the field that patent is in to decide whether something is likely to work in practice or whether it is just some bogus invention that has no chance of working.