Deve-se reescrever adicionando um dos verbos e também um dos phrasal verbs sem alterar o sentido das frases.

1 - Mark blamed me for the robbery. As the manager, I should have been on to the night janitor

be on to someone significa "estar em cima" de alguém, no sentido de estar de olho, estar atento a algo que a pessoa está fazendo de errado

2 - Janice refused our offer to split the check and insisted she was up to pay for dinner.

to be up to = estar disposto

3 - Julius apologized and said he was out of ideas

to be out of significa não ter mais

4 - Cassius promised me his word that he would be along soon.

be along = estar junto/também