Bobert.
whatever was on Martin's phone - unless it implicated that he knew Zimmerman and/or planned on hurting Zimmerman - is not evidence...

If it is not, the defence will not be able to use it, so why withhold it?

Richard Bridge, who is also an attorney, says it isn't evidence...
Richard Bridge may be an attorney, but he does not know what it is, so how can he state that?

But again, Keith... Why is anything that Martin did prior to being murdered relevant to the case???

The jury have to decide if M attacked Z.
They have to make a judgement on how he might behave in that situation.
His past behaviour is relevant.
Sorry, but it is.