What is the formal way to say ``clumsy text structure''?

Suppose we modify a constituent (e.g., noun phrase) with multiple modifiers of the same type (e.g., prepositional phrase). Can we say that this expression ``clumsy''? What's the formal word choice?

Clumsy is a perfectly acceptable adjective for poor phrasing. However, I'm not certain what you mean by 'formal' for word choice. Do you mean for use in academic settings or in literature? If you are seeking an adjective specific to poor language construction, I would opt for either ineloquent or inarticulate for either written or spoken language.

The links above to M-W are for the positive forms of each adjective, since the negative forms above will have unhelpful dictionary entries such as: ineloquent- Not eloquent, lack of eloquence.