Which phrase is correct: "Nice to hearing from you again" or "nice to hearing you again?"
Neither. Correct is:
There are two things to notice here:
The present participle of the verb (ending in -ing) should not be preceded by the infinitive marker to, and after the infinitive marker to you should always use the base form of the verb. So it should always be Nice to hear and never Nice to hearing.
Also, there is a difference between to hear and to hear from. The verb to hear just means that you can literally hear and understand what the other person is saying. The phrase to hear from means to start or renew a social relationship with someone. In this case, you're trying to say that it was nice to speak with someone again, and you're not focusing on the physical act of hearing, so you want to say "Nice to hear from you".
In English we would say
Note the "be" in there.
If you want to use hearing, then say:
This is quite common in email, phone conversation, or regular talk.
You could also say: