I heard a native speaker say this sentence
I use my phone to keep in touch with my friends asking them about homework.
I wonder why he said ‘asking’ instead of ‘to ask’. Is it a gerund?
I heard a native speaker say this sentence
I use my phone to keep in touch with my friends asking them about homework.
I wonder why he said ‘asking’ instead of ‘to ask’. Is it a gerund?
This line was spoken, so you of course couldn't hear punctuation. Written out, the best punctuated sentence without ambiguity is
I use my phone to keep in touch with my friends, asking them about homework.
Here "asking them about homework" is participial phrase and an adverbial modifying the previous action mentioned in the sentence. The subject of this participial phrase is "I". And the participial phrase supplements the main clause with more information. You can roughly understand the sentence as "I use my phone to keep in touch with my friends and ask them about homework."
You could use an infinitive instead, but it changes the meaning ever so slightly, because "to ask" here omits "in order". "I use my phone to keep in touch with my friends in order to ask them about homework." You see the little difference in meaning?
Grammar note
I lead with a point about punctuation but haven't gone into detail. Syntactically a participial phrase like this could modify an immediately-preceding NP or a different one. In this context there is only one parsing, but in other sentences there could be ambiguity. See FumbleFingers' comments for more details.