- I look forward to.
“Hear” is obviously not a thing, but a verb, so it does not make sense to “look forward to hear”. The thing you look forward to is “hearing” (“heard” by the person), and the phrase in question is thus:
- I look forward to hearing from you. (correct)
- I look forward to hear from you. (wrong)
This formal phrase literally meaning “I look forward to hearing from you” is used mainly in letters and email correspondence in places where in English we would use “I look forward to hearing from you” or “thank you in advance for your reply”. If we want to add some friendliness to the phrase, we can use the past tense:
- I am looking forward to hearing from you.
Most native speakers find the “am looking” form more informal than the “look” form.