People sometimes mistakenly write “looking forward to hear from you,” but this is incorrect. The correct phrase is looking forward to hearing from you.
The phrasal verb “look forward to” is always followed by a direct object, the thing you’re looking forward to. As the direct object has to be a noun phrase, it should be the gerund “hearing,” not the verb “hear.”
I’m looking forward to hear from you soon.
I’m looking forward to hearing from you soon.