Do bleed effects stack?

That is my question. I have a mesmer/ thinking about ranger - just for the pet. Will the ranger pet's bleed attack stack with conjure phantasm?

It should stack, however I'd reccomend "Hunter's Shot" instead of the pet attack.

Hunter's shot only works when the enemy is moving or knocked down (the bleeding part) this is very, very useful in PVP when everyone is moving, but for PVE, hunter's shot ends up being a cheap power shot alternative. It's a superior skill in many ways, but I wouldn't select it if your goal is to stack bleeding plus your "hex." You could stack bleeding,poison and your phantasm.

You are right, yet for 5 energy hunter's shot is a must, not to mention the long bleeding condition it inflicts. Beast Mastery has minimal usability so I'd ignore it completely.
I wouldn't say hunter's shot is just a powershot alternative in PVE: it's most useful when you are attacking. Just wait for the monster to start moving and shoot him.

If he's running a pet build, there's no reason why he shouldn't use the pet attack- it's hard to make skill recommendations if you don't know what attributes his character is using.

As for the question, yes, different sources of health degeneration stack up to 10 pips(20 health per second). 2 people causing the same degeneration(2 people inflicting bleeding, or casting conjure phantasm) won't stack, but bleed+conjure phantasm+phantom pain, etc works just fine.