As an ounce of prevention is worth a pound of cure I recommend those tiny rubber stoppers you see in the photo. They have a peel and stick part that goes under your case which retains the plug on a strip of rubber. That strip might wear out in a few years and rip, but they cost almost nothing to replace (and in fact come in packs).

Phones used to have these things built in, then they stopped in the smartphone era because they didn’t look as sleek and futuristic I guess. Now, if you have a case, it once again makes hardly any difference to the appearance.