call (or phone or ring) (somebody) back means return a phone call (e.g. I called the company back but the offices were closed for the weekend.)
call around means phone many different people (e.g. We called around but we weren’t able to find the car part we needed.)
call in (or drop in) means visit somebody for a short time without arranging to do this
call on somebody means ask for an answer (e.g. The teacher called on me for questions.)
call on somebody means visit somebody (e.g. I called on you last night but you weren’t at office.)
call somebody off means cancel it (e.g. Tom called the wedding off because he wasn’t in love with his partner.)
call somebody up means phone (e.g. Give me your phone number and I will call you up when we are in town.)
calm down means relax after being angry (e.g. You are still mad. You need to calm down before you drive the car.)
calm (somebody) down means become calmer, make somebody calmer (e.g. calm down. There’s no point in getting angry)