I have a very good solution for you. It won´t yield a superior one, but you have very good chances of getting a 3-socketed one.
1. Find a low quality/cracked/crude Phase Blade.
2. Fix it with the low quality weapon + Eld rune + chipped gem recipe. This sets the item level of the sword to 1, which is important for the next step, because Phase Blades with ILVL=1 can have a maximum of 3 sockets.
3a. Socket it with the "weapon + Ral rune + Amn rune + perfect amethyst" recipe. You have 2/3 chance to get 3 sockets.
3b. Socket it with the socket reward to be certain of getting 3 sockets.