Question

There seems to be some interference on the phone line. Could you speak __________?

a,louder
b,more loudly

Answer 1

could u speak more loudly.
b is the answer.☺️☺️

Answer 2

There seems to be some interference on the phone line.

Could you speak more loudly?

Here the right answer is more loudly as we are in continuous present tense.

Therefore more loudly is the right superlative which is to be used in this situation.

Hence the right answer is option 2 which is more loudly.