What I'm doing wrong?

[epixoip]

phpass is salted and iterated MD5. Wordpress uses a cost of 2^11 (2048 iterations) by default, so a single hash is 2048x slower than raw MD5. If you have two hashes with two unique salts, this would slow it down even further, making it 4096x slower than raw MD5. If you have 10 hashes with 10 unique salts, it would be 20,480x slower than raw MD5.