There are a couple different ways to do what you’re saying. For now, we’ll say the Photoshop layer with the Illustrator item you want to use as a mask is called Clipper.
Command/Ctl-click on Clipper’s thumbnail in the Layer palette. That will create a selection in the shape of the opaque pixels of the layer. Then choose the layer you want to mask and click the Add Layer Mask icon at the bottom of the palette (looks like a white box with a dark circle in the center). That will create a mask on the new layer in the same shape as Clipper.
Orrrr… Place Clipper below the layer you want to mask. Hold down Option/Alt and place your cursor between the two layers. Your cursor will change to a box with a downward arrow. Click and you’ll create a clipping mask with the top layer only showing up where Clipper is opaque.
One final note: You might find more flexibility saving your Illustrator files as AI files, and then in Photoshop choosing File>Place… and placing the AI file. That creates a Smart Object that you can scale and manipulate with Photoshop re-rasterizing the source info to keep a constantly clean image. Plus you can change the Smart Object in Illustrator (in Photoshop, choose the object layer, right-click, and choose Edit Contents) and the changes will ripple back to Photoshop.
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It is easier to destroy than to create.
More fun, too.