Low PSI on Pool Booster Pump

I have a Magnetek 1081 PB4 Booster Pump, 3/4 hp, 3450 rpm - part #173840-20 attached to my pool to run a pool cleaner. I recently replaced my Polaris 380 with a Hayward Phantom only to discover that the Phantom won't run properly because it's only getting between 11 and 12 PSI from the booster when it requires between 20 and 25 PSI.
The instructions that came with the Phantom says that it requires a 3/4 hp booster pump so I'm trying to figure out why I'm not getting enough PSI to the cleaner using this pump. The pump is about 25 feet from the pool's wall connector and then about another 20 feet of hose to the cleaner so a total of 45 feet from the pump to cleaner.
My questions are: 1) How do I calculate how much PSI this pump is capable of 2) If anyone has any ideas as to how to increase the PSI 3) How big of a booster I need to get 20-25 PSI at 45 feet
Thank you very much. Stu
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