When you pronounce the phrase 'pick it up' as a native speaker, is
there any word in it that need to be pronounce higher in pitch with
more stress?
There are a few ways one could mean the phrase:
"Pick it up!" as a command that could be given to remove something from the floor or increase one's speed as in a march where someone may tell the person in last place to "Pick it up!" Parents could tell their children to "Pick it up!" about stuff left on their bedroom floor.
"Pick it up?" as a question where the "up" would have a rising intonation as it is meant more as a question than anything else. Someone may see money on the ground and give the line, "Should I pick it up?" that is a question rather than an order or statement.
"Pick it up," as a statement that when commenting on a sports play there can be the call of, "Pick it up," even though the play is taped and there isn't anyone to take what could otherwise be seen as an order. There are also card games like Euchre where this phrase may be used in play when someone wants to order up the turned up card to make it trump.