The phrase "I saw" can be replaced by several synonyms, depending on the context and the writer's intended meaning. Some of the common synonyms for "I saw" include "I spotted," "I observed," "I witnessed," "I noticed," "I detected," and "I caught sight of." "I glimpsed," "I beheld," "I took note of," and "I laid eyes on" are other alternatives. Each of these synonyms implies a slightly different nuance or tone, and the choice often depends on the writer's style and preference. However, it's useful to have a variety of synonyms in one's vocabulary to avoid repetition and add interest to the writing.