Phased cloaks are banned by treaty.
Which treaty any sane government would have said adios to in the face of the Dominion threat. Or the Borg, for that matter.
And--as far as I'm concerned--phasing isn't cloaking. Not going to get into that again in this thread, but it isn't cloaking any more than a replicator is a warp drive.
And the phase cloak doesn't need to be stable to be adapted as a phasing weapon. Then that wholly inapplicable treaty would never have applied even in the minds of folk who think laws and treaties aren't open to interpretation.