I'm glad you posted a picture. Your tank is very scarcely decorated with a very small reef structure. You will be very limited as to how many fish due to the likelihood that the established fish will become territorial towards new fish.
In the current situation I think you have room for 1 more fish. Your live rock structure being small will limit the supply of microfauna, copepods, amphipods, etc. This limits your fish selection and makes a Dwarf Angel a bad idea, and probably makes a Blenny a bad idea as well. I would suggest a Hawkfish, which diet you can easily provide for with a variety of frozen and freeze dried foods. A Flame or Longnose Hawk will be fine with your existing fish. These are not aggressive species. There are a couple of Hawkfish which get a bit larger and become territorial, but they aren't for your tank anyhow.
As for phosphates, they can be an issue yes. But I would never suggest that you stop feeding the fish to reduce phosphates. Instead, you should measure the phosphates in your water supply,and makes sure that you are cleaning any filter pads DAILY, or remove the filter pads entirely.
In any case, phosphates are a very minor concern for your current tank. Very minor. Right now, at worst, they will make it difficult for coraline algae to take hold.
One more point about your reef structure. These are small fish you have. You have no need for large cave openings on the back side. These large openings cause stress for fish at night because they do not feel secure. I would suggest adding some more rock, and begin by nearly closing off the back of those cave areas. You could use these rocks as building blocks to increase the height and base of that reef, without having to move your decoration. If cost is an issue, check out www.marcorocks.com
. I use the Key Largo dry rock.