“S’en aller” is an idiomatic verbal locution in which “en” has lost its usual meaning: it means nothing in particular nowadays, but it must be kept as an added particle so as to have the meaning “to go away”. “Je m’en vole.” is an error: the verb is the verb “s’envoler” and you never separate the prefix “en” from the root; you always write “Je m’envole.”. Here “en” is a prefix, not a preposition. Therefore you shouldn’t get the idea that “en” is combined with verbs so as to produce phrasal verbs. There aren’t any phrasal verbs in French.
Also, the translation of “Je m’envole.” is not “I am flying away.”. In a plain context you’d say rather “I am taking to the air.”, “I am taking off.”.

In the context of air travel, then yes, you can translate that way, but the simple sentence is not used in that context: it must be modified by prepositional phrase the complement of which is the name of a location you are going to.

• Je m’envole pour Hong Kong demain.
  (I am flying away to Hong Kong tomorrow.)

“Je vole.” would be “I am flying.”, though. But if you want to say “I am flying there tomorrow.” in the context of air travel you have to say “J’y vais demain en avion.”, not “J’y vole demain.”.