Can I use a iPhone4s microphone in iPhone4, cause iPhone4 mic broken

No. If you really wanted to replace the microphone that way you would need to manually remove the microphone from the part itself from the other phone.

You are better off buying the replacement parts as the assembly wont fit as a whole.

If people can not hear you during calls then you will need to replace the charging dock assembly.

You can get the charging port dock assembly here:

[linked product missing or disabled: IF182-009]

Guide to replacing the part:

iPhone 4 Dock Connector Replacement

If people can not hear you during calls on speaker phone then you will need to replace the top microphone which is usually together with the sleep / power button ribbon assembly.

You can get the part from here: [linked product missing or disabled: IF182-015]

Replacement guide for part: iPhone 4 Power & Sensor Cable Replacement