If I knew his number, I would phone him. (but she doesn’t know his number) Tom would read more if he had more time (but he doesn’t have much time)
We use the past in the same way after wish (I wish I knew/I wish you were etc.). We use wish to say that we regret something that something is not as we would like it to be:
I wish I knew Paul’s phone number. (= I don’t know it and I regret this). Do you ever wish you could fly? (you can’t fly). I wish I didn’t have to work. (but I have to work).
After if and wish, you can use were instead of was (if I were/I wish it were etc.).
You could get a job more easily (you could get = you would be able to get) if you could speak a foreign language. (you could speak = you were able to speak).