

If the question is "I need to be on the paper" - that's easy. Tell your PI you put in work and you should be on the paper.
If you want to be first author - did you do most of the work? Was the idea yours or were you just a grunt in the lab carrying out the basic labs and collecting data and handing it over to someone to analyze/draw conclusions?
If you are an undergrad working under a new PI or a grad student, be thankful they give you 2nd author.
Also, any author after the first 2 are basically alphabetical order or whatever - no one cares. Last author is usually the PI.
There are some cases where the PI will do most of the bench work and put a trainee who contributed a figure or two as first author so the PI can be the senior author. These people are lucky.
... and I have NEVER seen a PI do bench work.
My PI ALWAYS puts himself as first author 🙄
PIs do not, and should not do bench work - they need to focus on their jobs - get us (PhD students / postdocs) funds / collaborations to advance the project. Bench work is grad students' responsibility. However, I still saw some micro-managed PI, who loved to go over experimental plan / help with bench work.
I wouldn't say that PIs should not do bench work. It depends greatly on the style of the individual PI, as well as the assay. I know full professors who do it regularly, and they have 10+ member labs.
He is a PhD. It makes pretty close to zero sense, but his choice I suppose.Just to say that if your PI is an MD this is more common. If your PI is a PhD it is exceedingly rare unless something happens where another PI refuses to take anything but last in a collaboration but it's really your PI's lab that did all the work (yes I've seen this happen when people collaborate with big names in the field and egos are involved)