We present an upper bound on the minimum Euclidean distance d_{Emin}(C) valid for any linear and non-linear block coded PSK. There are several well known block codes that satisfy this upper bound with equality. With given parameters; the alphabet size q, the blocklength n and the number of codewords |C|, it therefore follows that these codes are best possible in terms of minimum Euclidean distance. We furthermore establish a lower bound valid for Gray coded binary block codes. The minimum Euclidean distance is bounded from below by the minimum Hamming distance of the corresponding binary code. For several Gray coded binary block codes the upper and the lower bounds coincide. It can then be concluded without calculating the minimum Euclidean distance that these codes are best possible.