Final answer:
Gloria can best enforce Phil's promise through promissory estoppel, as she relied on his promise and quit her job, making his promise enforceable because it is supported by consideration.
Step-by-step explanation:
Gloria's situation involves a principle in contract law called promissory estoppel. Essentially, when one party reasonably relies on the promise of another, particularly if it involves a detriment, the promise may be enforced by law to avoid injustice, despite lacking a formal written agreement. Therefore, the correct option is that the best way to enforce Phil's promise is to assert promissory estoppel.
Phil's promise can be considered enforceable because it is supported by consideration, with Gloria quitting her job as the consideration. This action shows a clear reliance on Phil's promise, thus fulfilling the requirement for promissory estoppel. Furthermore, asserting unreasonableness for Gloria's actions or stating that all unwritten promises are unenforceable are not accurate representations of the law as it pertains to this situation.