Making a phone call isn't always easy - especially if you don't know the person on the other end of the line very well... Here are some expressions you can use if you're on the phone:

-Hello, is that ...?
-Can I speak to ..., please.
-Hello, this is ... calling from ... in ...
-Could you ask ... to call me back, please?
-Thanks for calling back.
-Good morning, I'd like to speak to ...
-Is ... available, please? My name's ...
-Could you give ... a message, please?
-My number is ...
-I'm so sorry, I've got the wrong number

-speaking.
-Oh hello, ..., this is ... speaking.
-I'm afraid ... is in a meeting/ not in the office/ still at lunch/ on holiday this week/ away today/ not available just now...
-I'll just find out if ... is in the other office/ available/ back yet.
-What's your (extension) number?
-I'll put you through to ...
-Can I get ... to call you back?
-Hold on a moment, please.