It shouldn't affect the stiffness, however I'd be a little cautious about using phenolic. In the number of bows I've made I've only had one delamination issue and that was with an accent stripe in the limb wedge. My issue was dissimilar materials and the wood fibers actually sheered, not a glue failure. Since the limb wedge actually flexes, unlike phenolic in a tip overlay or riser, you may see the same issue. If you're going to give it a try I'd suggest only using solid wood and don't compromise your feathering.