One of the loading screens proclaims that phaselocking the same enemy multiple times results in "diminishing returns". I've never particularly noticed this effect myself, but I find I rarely phaselock the same non-boss enemy twice, and if I phaselock a boss it's mostly "just because", the damage you deal to enemies you can't "lock" in place is minimal at my level.
What exactly are the diminishing returns? I assume Phaselock does less damage/doesn't hold as long, but what's the formula for it? Does it affect skills like Ruin and Helios which do extra damage upon Phaselocking as well?