The meaning of the Greek text of this phrase is not clear. Possible meanings are 1) "The Pharisee stood and prayed about himself in this way" or 2) "The Pharisee stood by himself and prayed."
Robbers are people who steal from other people by forcing the other people to give things to them, or by threatening to harm them if they refuse to give what the robbers ask for.
The Pharisees believed that tax collectors were as sinful as robbers, unrighteous people, and adulterers. This could be made explicit. Alternate translation: "and I am certainly not like this sinful tax collector who cheats people" (See: [[rc://en/ta/man/translate/figs-explicit]])