This phrase means "You should decide." You say this to someone when you think that they should be the person to make the final decision about something.
For example, you might say this to your boss who doesn't seem satisfied with the work that you've done:
A: Hmmm... I'm not sure about this. I don't think we should release it to the public yet.
B: OK. It's your call.
"It's your call" is similar to:
But "It's your call" carries more of a sense that this person has the responsibility or right to make the decision. In other words, that person should do it.
"It's your call" is also similar to this phrase:
It's your decision.
But "call" is more casual than "decision".