Barring a rash of injuries the Phillies don't really seem to need a low-leverage relief arm over the next five weeks, except maybe as chum in September when the games are meaningless (though they'll also have to figure out how to get Nick Nelson and Kolby Allard a few starts in that case). There's no reason for Ruiz to lose that spot to an unknown quantity, and Mercado and Phillips are also options along with Marte. If they go six-man that's one less spot; if they don't, Turnbull is a reliever again.
There are few trade candidates who'd be an improvement in high leverage situations, they'd have to be significantly better than Soto, Alvarado and SD to have value in that role.
There are, in fact, more than enough trade candidates who'd be an improvement over those guys (though I'm also not prepared to overrate Soto or underrate Alvarado). The question is do the Phillies want to pay the price - and maybe even win a bidding war - for one of them? Kirby Yates is a fashionable name lately, if he's actually available. Along with Scott. And Miller who I don't really consider a serious option.
Where it gets tricky is if you're just looking at guys who are about the same. Then you are just adding another guy to the 5/6/7 tier and hoping one of them ends up sticking as the best 5th option in October (while deciding neither Ruiz nor Turnbull are candidates for that chance).