It's pH, not PH. PH = PowerHead, pH is the measurement of how basic or acidic a substance is. Alkalinity is the resistance of a liquid to change pH.
pH should be 8.2 to 8.3 constant from day to night. The use of a refugium, algae scrubber or another tank on an opposite lighting timer will keep it steasy. I recommend an algae scrubber, but I am biased.
Phosphate should be as near zero (0) as possible on a hobby test kit.
Alkalinity should be kept pretty high at 4.5 to 5 mEq/L (Miliequivalents per liter) or another measurement is 8-12dKh (Degrees of Karbonate Hardness) dKh is a German scale measurement. Keep it high as you can and as stable as you can. Usually a lot of live rock, a good amount of internal water flow, and adequate gas exchange will keep these numbers pretty constant. Over time your calcium and alkalinity will drop without proper water changes. I like to play around with my tanks chemicals, so I either dose a two part calcium and alkalinity buffer or I will most of the time drip kalkwasser. Do not use kalkwasser (limewater) unless you have thoroughly done your research first. You also shouldn't use a two part solution either unless you have a complete understanding of the chemistry involved and the test kits for it.
To cover my butt, I'm going to go ahead and say it... "Do not dose what you can not/do not test for."