There is air in my pump. I cannot prime it after having done a backwash.

You may have a vapor lock which is a bubble of air that is stopping the pool pump from priming. Is there anyway to bleed off the air

your pump will not prime with air in the line. Check the impeller for junk in it. Clear it out by opening the pump lid, and then opening the air bleeder on your filter. That will flush the stuff from the impeller. Check pump lid gasket, and make sure all your baskets(skimmer, and pump) are empty. Prime pump. That should get it flowing. Also, clean or backwash your filter.

1. Open air relief and drain plug to allow air into filter and water out.
2. Take apart filter, remove all nuts/bolts/screws/fasteners and separate the filter. Could need some force to separate
3. Use a shop vac to suck out the sand or a cup, be careful not to be too violent, if you damage laterals sand will go into the pool
4. Check the laterals, No cracks or damage
5. Close drain plug.
6. Go to pool/home store buy POOL SAND. Amount required should should be posted on the filter somewhere. any extra will go into pool, or backwash out.
7. Add some water about halfway of the filter, slowly add sand back into filter, dont be too violent. be careful not to get sand into any piping it will go back into pool.
8. Prime the pump(add water to it) backwash the filter for 2~3 minutes
9. Close air relief
10. Run pump on normal open air relief as need to let excess air out .

Done!

Your hose either has a hole in it, at the sections at the waters surface where it is exposed to the air? Even a "Pin" hole will create the symptom you are experiencing.
Or... there is a clog in the unit itself.
It appears that you are either sucking in air, or the water flow is being blocked. The pump should pull water no problem through a vacuum hose or a suction style pool cleaner. If the pump loses prime, then "Water" flow is being restricted either physically are mixing with air.

Does it show pressure when in "Filter" mode?

If not, then your pump is either not primed, Impeller is plugged, or there is not enough water in the pool, you are sucking air.

Does it filter? Does the pump have full prime? I'm not clear about how when the valve is put in the backwash position nothing happens.

Pumps don't need to be backwashed, some filters do. Sand and DE filters need to be backwashed when the filter pressure has increased to 10 or 11 psi. depending on the manufacturers recommendation. The cartridge filter cannot be backwashed but instead it is removed and a hose sprayer is used to clean out the dirty outside. Your pump does need to be primed so it is not trying to pump mostly air. Each time the pump basket area is low in water then it needs to be primed. You will know how low it can go before it needs to be priming by turning it on when it is low and if it cannot start pumping water at full rate then at that level of water it needs to priming. If it is pumping water at full flow and you turn it off it should not need re-priming because there is enough water in it to force the air through the system. I hope this helps.

SOUNDS LIKE YOU HAVE A SUCTION LEAK , CHANGE SHAFT SEAL AND WHEN YOU START PUMP RELIEVE AIR OFF OF FILTER. THIS HELPS PUMP PRIME FASTER

is your 'pumps' skimmer box 'O' ring in good condition?

do you have a hole or loose pipe work?

Try priming your pump and running it for a few minutes in the normal way, and switching it over to backwash quickly. You may be loosing prime. DO NOT RUN YOUR PUMP IF YOU DO NOT SEE WATER IN THE PUMP HOUSING YOU WILL DESTROY YOUR PUMP. Please rate me if you find this helpful, thanks.