The thing is, stabilization really does need to happen either while you're recording or after - there's no magic middle ground, so whoever suggested otherwise was being a bit optimistic. That said, the earlier answer about your phone's built-in stabilization is spot on, and I'd double-check those settings because it makes a huge difference. Beyond that, your best bet for prevention is actually shooting technique: hold the phone with both hands, keep your elbows tucked in, and move your whole body with the action instead of just your arms - I learned this the hard way filming my kid's skateboard attempts in the driveway and it changed everything. If the damage is already done on footage you've shot, you're looking at software no matter what, but even the lighter apps in the App Store (not the desktop juggernauts) can do quick stabilization if you want something simpler than what's been mentioned.