It is a tiny ( pan head ) machine screw, and a white rubber plug
The plug is not needed ( but you will need THREAD LOCK )
Take your camera off ( from anti-jello balls, and unplug BOTH CONNECTIONS ( servo plug, and power plug )
Take it to ace hardware, the screw is approx ( 1/8 inch wide, but don't know EXACT size?,
And 4mm long )
You will have to fine one that fits the thread size at hardware store!
Since you do not have rubber plug, you will need thread lock on screw before instal
( tighten screw all the way, then back off 1/4 turn )
( this is where rubber plug comes into play )
It does 3 things
1) make the phantom look finished ( cosmetically )
2) keeps dust/dirt out
3) keeps screw from falling out ( should it come loose )
Which sounds like what happened to you!
Thread lock will work just fine!
As for replacement parts ( try classifieds ( here ) maybe someone has a wrecked phantom vision
And will help you with parts? )
Jerry D
USA
( J Dot )