Learn Italian: Se questo mobile è inutile, devi buttarlo via definitivamente. - If this piece of furniture is useless, you must throw it away permanently.

In Italian phrasal verbs (like buttare via, to throw away), object pronouns must attach directly to the verb, never to the adverb. You drop the final -e of the infinitive to make buttarlo, leaving via as a separate word. You can never say buttare vialo or buttare lo via.

Since devi is a modal verb, could the pronoun go at the very beginning of the phrase?

Yes! Just like with regular verbs, when you use a modal verb (dovere, potere, volere) plus an infinitive, the pronoun can move to the front. You can say lo devi buttare via, which means exactly the same thing. Notice that the adverb via stays in its place at the end of the verbal phrase.

Is mobile a false friend here?

Yes. As a noun, un mobile means a piece of furniture, not a mobile phone (which is un cellulare or un telefonino). Since it is a masculine noun, we use the masculine pronoun lo to replace it in the second half of the sentence.

Does the meaning change if I just say buttarlo without the via?