Parsing the sentence

My friend never forgets to call/calling on my birthday.

Dear Teachers!

Could you please tell me whether “call on” is phrasal verb in this sentence or the preposition on has nothing to do with the verb call and is related to my birthday?
Could you help me to parse this sentence?

Thanks in advance.

It is “call” (visit) + “on my birthday”.

With call in this sense, which form is proper then: Gerund OR Infinitive?

My friend never forgets [size=150]to call/calling[/size]…

“never forgets to call” is the natural form.