Can surgery for gsstric bypass, peg tube placement or central line damage the phrenic nerve?

Yes. Placement of a central line, in the neck, may damage the phrenic nerve, although this is highly unlikely.
Not really. I have never heard of phrenic nerve damage from any of those procedures. The gastric bypass and peg tube take place below the diaphragm - away from the phrenic nerves. Endotracheal intubation with those procedures is in the throat, but interior and away from the phrenic nerves. Central line placement (in the internal jugular vein) could potentially injure a phrenic nerve, but i've not heard of it.
HIGHLY UNlikely. The phrenic nerve is from above the diaphragm and the procedures your mentioned are all below this level...