There are many synonyms for the phrase "is plain" which can be used to describe something that is simple, clear, and uncomplicated. Some of these synonyms include words such as "clear," "basic," "simple," "straightforward," "uncomplicated," "unadorned," "unembellished," "undersized," "meager," and "unimpressive." These words are often used to describe things that are straightforward and easy to understand without any additional explanation or embellishment. Using synonyms for "is plain" can help to add variety and depth to your writing, while still conveying the same meaning. Ultimately, whether you choose to use the word "plain" or one of its many synonyms, the goal is to express yourself clearly and effectively.