How sure are you that it is actually a-PHP? Because a-PHP is a now a schedule 1 drug and is even banned in China, so it has become rare. The closely related drug a-PHiP however is commonly available and is widely legal. As a resul, chances are you, especially if you're in North America, that what you actually have is a-PHiP.
From what I recall a-PHP was more potent than a-PHiP, but never are best taken orally. These substances shine when vaporized. But at the very least I'd go with intranasal.
Neither are acutely toxic, meaning that a large dose of either is unlikely to result in complications. That said, at 5'11" and nearly 300 pounds, your body mass index is quite high, so I wouldn't push the envelope to be on the safe side.
As with all unknown substances. Take an allergy test dose perhaps sublingually, like a milligram or less (in case it happens to be a potent psychedelic mislabeled). Wait a number of hours or a day even, then try 5 mg, etc.