How about an extended-range Phoenix with a ramjet sustainer? Use on of your tandem-boost configurations, then add some air intakes to the main missile. You could make the intakes by having circular intakes in between the wings (SA-6 style), incorporated into the wings (AS-17/SS-N-22 style), a pair of side intakes (ASMP style), box intakes replacing two of the fins (Meteor style), or maybe just bridge between the fins with a flat plate. An alternative to the tandem-boost layout would be to have the booster within the original length of the missile and add a pair of side-mounted complete ramjets (Bloodhound style).
Moving away from Phoenix technology, but still buildable from Phoenix models, I can up with this idea for a British AAM using scaled-down Sea Dart technology:
Top version is the original Phoenix, middle one has the wings turned around and the control fins cropped, bottom one was new Red-Top-ish wings. In both cases, the nose is cut off and used as the centrebosy of the air intake.
Another simple idea for Phoenix models is to scaleorama 1/100th or 1/144th ones into 1/72nd as advanced version of the Falcon.