Why is it that handicapping causes so much angst?. I've sailed in IOR, MORC, IMS, IRC, ORR, ORC, ORR-EZ, PHRF,and OD. They all have good and bad points. For most of us, racing is recreation, not blood sport.
I sit on a local PHRF board. I can't speak for the OP's area, but they should have clearly defined bylaws and processes that detail how their handicapping review and adjustment process works. As has been stated above, read the rules. Understand the process. This is absolutely critical, both from understanding what your role is, and making sure they do what they said they were going to do. This can't be overstated. Period. Also, understand that you are dealing with people, not a black box formula. If they are not following their process, you are entitled to point that out, preferably in a calm and professional manner. This process does not have to be adversarial.
If they have decided to adjust your rating, you should be entitled to review their supporting data and rationale for the change ahead of time, which gives you time to prepare your case to refute the change. Be factual, provide data that is clearly labeled, in the format they are looking for, and relevant to what they are presenting as the basis for the change. Bring enough copies of your presentation for all those present. Provide consistent data, don't include the drifter day where you finished twenty minutes behind with data with more consistent conditions, this just skews things and is relatively easy to spot. Also understand that in many cases, we sail in your fleet. We see your starts, tactics, trimming, boat handling. Stating something like "my starts would make T Hutch cry", or "my sets and gybes are flawless" isn't going to go far when the person you are telling it to sees your starts, sets and gybes every week. Be honest, point out where you think you are good, and not so good. PHRF assumes that your boat is well prepared, well sailed, well equipped, and is not going to to give you a break because you may not start well, or your #3 is older than you are. The intent is to rate the potential performance of the boat, not to golf handicap. Be clear, stick to your points, know the data you are presenting thoroughly. Know how much time you have, for the love of God, stay on point, and don't wander. Be prepared to answer questions about the data you are presenting, your boat, your crew. Leave enough time for questions. Please don't read from it verbatim. Make concise, salient conclusions that are clearly supported by the data you provide.
As has been said, PHRF is data, and performance driven. It is not a measurement rule, although measurements do matter. It is not a VPP based rule. Production boats with large runs provide lots of data points and are easier to handicap well. Custom, one off, modified boats are harder. Race results are what matter most. Make sure that you have, and that whatever measurement data the review board has is accurate. For production boats, check the ratings other PHRF areas (with similar conditions) have for your boat, how many boats are racing there, and when the last time that rating was adjusted. While PHRF is not a measurement rule, measurements are taken into account, and do matter. If your boat is 400 lbs heavier than they think, bring that up, with supporting documentation. Make sure your sailmaker has current sail certificates for you.