Exterior shower problem

[DennisB]

Hi,
Had a leak in the fittings that connect the water supply to the exterior shower faucet. Took it apart, reconnected -no more leak.
When I turn the faucet on now, the water flows well, but there is a stream of water coming out of the little white port that is next to the faucet handle.
(Photo attached) what is this thing and why is it happening?

Thank you for any info or suggestions
Dennis