As you now know, the internals are only accessible if you open the main boxes. This is one of the big advantages of the double hose regulator, in that no water actually gets to the first stage and second stage inside the boxes. I’d venture to say that probably the IP and cracking pressure are already where they should be, and that until you have some experience with the double hose regulators that you don’t need to adjust anything right now. But there is a lot of expertise here on how you can do so, if needed.
Welcome here, by the way. It’s good to see a new member come in. There are a lot of people here who can help you out with any problems. How are you planning to dive your Phoenix/HPR double hose? Single tank/double tanks, what BCD are you using, etc. All these can have a bearing on the positioning of the double hose box, which should be between your shoulder blades when in the water.
John C. Ratliff Diving since 1959, at age 13. Haven't stopped, and still enjoy getting wet.
Welcome to the board. A good friend and board member designed the Phoenix and the HPR. I made the first prototypes of the HPR and dove them in early testing so we can help you with it. Setting up a USD DH with a Phoenix and HPR is really not that much different than a single hose reg, set IP to what you want, I use 135 psi, I set ALL my regs to that so I don't have to keep up with different setting and have to figure out what was set to what. Then screw in the HPR BY HAND till it seats then back out so the next hole is pointing down the horn, usually 1/3 to 1/2 turn. You can do more but you stand the chance of making the cracking pressure too light. In any case, make sure one of the holes is pointing directly down the supply horn, if not, the venturi action of the reg will not work. Pressurize the reg and make sure there is some play in the lever, adjust the nut, this will cause the lever to lift. Stop when the lever is about even with the ledge of the back can, set the diaphragm on it and check for about 1/16 to 1/8 inch of space between the lever and diaphragm by gently pressing on it listening for contact. If you press it too far it WILL slam the diaphragm down and go into a strong freeflow, this is normal, scares the crap out of you but normal. Set the top can on and squeeze the together hard, if you start to hear some freeflow, drop the lever a little. I tend to put in a little more distance when the seat is new since it will take a set and raise the lever some, saves me from having to go back in later.
Everything you need to know about the Phoenix/Aquamaster is available at vintagedoublehose.com. Any knowledge you can accumulate on Conshelf first stages, Aquamaster DH, Royal Aquamaster, Argonaut Kraken, will help you understand what you have.