On a telephone call, identify yourself with "This is ___":

Hi, this is Aaron Knight. Can I speak with Mr. Jones please?

Don't say "I am ___." That's a good way to introduce yourself when you meet someone for the first time in person, but it's not correct for telephone conversations.

When someone asks to speak to you on a telephone call, and you want to tell them that it's you, use "This is he/she.":

A: Hi, can I speak with Masahiro Tsukada?

B: Yes, this is he.