The phrase "am one's obligation" suggests a sense of duty or responsibility. There are several synonyms that can convey a similar meaning, such as "am one's responsibility," "am accountable," "am obligated," "am duty-bound," and "am obliged." Each of these words highlights the idea of being bound by a sense of obligation or duty. When we say "am one's obligation," it generally means that we have an obligation to fulfill a task or responsibility that has been assigned to us. By using these synonyms, we can convey the same sense of responsibility and commitment while using more varied and descriptive language.