Translation:Call me immediately after you have met him.
Native English speaker here. This sentence makes sense. The person is telling the other person to call them a certain time. When? After something has happened, thus the need for a tense in the past.
See here: http://www.englishpage.com/verbpage/presentperfect.html. The present perfect tense is used for a time period in the past, not the present, thus it is applicable here.
I'd have said that "to phone [him/her/me]" while not quite as common as "to call [him/her/me]" was nevertheless far more common than "to telephone [him/her/me] but apparently my sense of usage (at least in print] is off. "To call" is far, far, far more common, with "to phone" and "to telephone" a distant second and third, respectively. So, yes, telephone should also be accepted.
One of the ngrams: https://books.google.com/ngrams/graph?content=to+call+me%2Cto+phone+me%2Cto+telephone+me&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cto%20call%20me%3B%2Cc0%3B.t1%3B%2Cto%20phone%20me%3B%2Cc0%3B.t1%3B%2Cto%20telephone%20me%3B%2Cc0