Foot Valve = Backflow Valve...
It sounds like your "foot valve" is leaking. Debris may have damaged the thin rubber seal inside, or it may have merely picked up a pine needle. (!)
Especially since the lakes are still lowering this late in the season, I'd add more hose to get the valve into deeper water. Use a milk crate and "zip" ties to get the valve clear of the bottom. Horizontal operation of the valve is OK.
The hose can be readily cut with a "bypass limb-lopper", which you may already own--stored away with your garden tools.
As you suspect, running the pump "dry" can damage the bearings. This will result in noisy operation or failure; however, the water already "up-pipe" could have kept the pump wet and cool-running.
To readily install a new foot valve, the hose should be heated. Dip the hose end into a pan containing very hot water.
Priming the pump can be done with a garden hose and a small "utility pump" ($60) immersed in a six-gallon bucket of water. "Crack open" the bleeder valve first.
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