Throw away your dictionary! Dictionaries are almost useless when it comes to phrasal verbs. Phrasal verbs are about a lot more than simply the definition that you find in a dictionary. The key to understanding the use of phrasal verbs is 'collocation' - what other words they combine with, and what contexts we use them in. I was late for work because I was held up in traffic. I didn't want to spend all my money at once, so I held back a few pounds just in case. Don't just think about the 'meaning' of a phrasal verb in isolation, or the translation into French. Try to learn them the way that native speakers do - in context, and in complete sentences.

Held up means that something makes someone late. So, for example: I was held up, and arrived late to the meeting. Warning: "Held up" can also mean "robbed." This is used when a person has a gun or a knife and robs you in the street. It does not mean when someone steals something without you knowing. Held back can have multiple meanings. First, held back can mean not passing in school and being required to repeat a year. For example, a child does poorly in 5th grade and has to repeat 5th grade. That child has been "held back." It can also mean "to limit." For example, "I held back my complete strength when I hit him so that I wouldn't kill him." Another example, "I was always successful in business. However, my family held me back. I would have spent more time working and been more successful if I didn't have a family." It can also mean "not to act/to be physically restrained." For example, "I was going to hit him, but my conscience held me back/but my friends held me back." The first, you did not act. In the second, you were physically restrained. I hope that helps!

"Held back" refers more to being unable to leave a place, not as much to being unable to arrive or late to arrive. When you are in traffic you have already left one place intending to travel to another place, so it would be kind of incorrect. "Held up" doesn't really make that distinction. You could be "held up" before or after you leave.