when we use this sentence

[n3wb1e]

when we use this sentences or what this sentences mean ?
1) i forget to phone him
2) i forgot to phone him
3) i've forgotten to phone him

thank you very much for your help

[Mister Micawber]

.
1) I forget to phone him-- Every day, I forget to phone him.
2) I forgot to phone him -- Yesterday I forgot to phone him.
3) I've forgotten to phone him -- I have forgotten to phone him every day so far this week.
.

[n3wb1e]

thank you sir, may i ask one more , so if i forgot to phone him just 5 minutes ago,i meant not so long.
is it correct if i use past tense ?

[Hamburg]

Yes, that's correct.

[Mister Micawber]

.
Either past or present perfect will work, n3wb1e, unless you specify a past time point:

I forgot to phone him.
I forgot to phone him 5 minutes ago.
I've forgotten to phone him.
(X) I've forgotten to phone him 5 minutes ago.
.

[n3wb1e]

i see, thank you very much sir for your help