I think there's a big distinction between ESL and non-English speakers.
"Name" is undoubtedly one of the first words someone learns when learning a new language, so there should be no concerns there.
"Email", if not understood from a language standpoint, can be conveyed by putting an email address in placeholder text. Unless this is the first online form the user has ever filled out I trust they will understand the meaning.
The same applies to "Phone Number" - Placing a properly-formatted phone number in the field will tell the user what is expected in that field.
The only tricky one could be "Message", which I actually suspect is most likely to be a "Question". "I have a question" or "What is your question?" is also likely to be understood by someone with an elementary understanding of English.
If your users are typically native speakers of the same language you could easily provide English/Native labels. For spanish, it could be
"Message/Mensaje" (or "Question/Pregunta")