It's not that you 'can't place pronouns after any phrasal verb'. It only happens with certain ones.
There are two types of phrasal verbs:
- prepositional verbs
- particle verbs
If the construction is verb + preposition, the object, noun or pronoun can't split the phrasal verb:
- You should stand by your friend¹
- You should stand by him
- *You should stand your friend by.
- *You should stand him by.
These constructions are wrong because the preposition must come first to introduce the prepositional phrase.
If the construction is verb + particle, the object can split the phrsal verb if it's a noun, and must split it if it's a pronoun
The last construction isn't used because the
it causes confusion.
Over could be interpreted as a preposition, which it isn't. Since there isn't an NP to disambiguate that
it is a matter (and not a table), we place the pronoun before the particle.
EDIT: I should make it clear that you can't put a pronoun after a particle verb.
@Mari suggested that both of these are right but mean different things
- "He looked me over"
- "He looked over me"
Both are correct, but only the first one uses the phrasal verb 'look over'. The second sentence doesn't have a phrasal verb, and uses 'look' and 'over' in their normal senses. The construct has a valid meaning in this case, but it might not be so in case of every particle verb.
Essentialy, if you add the pronoun after the particle, it would either be nonsensical or mean something completely different than the phrasal verb sense intended.
by is a preposition here, introducing the PP 'by your friend'
over is a particle here, because it does not take a complement