Translation:She is talking on the telephone while watching her son.
How can you tell what "en' means? Simply by using context? Because I've seen it translated "by" or "while", which have totally different meanings in English.
Prepositions like "en" don't really have a single meaning, you just have to learn the context in which it's used. In this sentence, it means that she talks on the phone and watches her son simultaneously.
Je vous en prie ! :)
Mais j'ai peur que l'on ne peut pas le dire comme ça (I'm afraid you can't say it like that). ;) The most common way to say "Thank you [very/so] much!" is "Merci beaucoup !" Other favourite alternatives of mine include "Merci bien !", "Mille mercis !", and "Merci infiniment !" Plus many others, depending on the context.
I have written telephone before and your translation has given phone. Be consistent or accept that both are correct.
Both are accepted now, but changes can take several days to show. Unfortunately there's nothing we can do about it but wait and be patient.
If you have "phone" rejected before 4 April, 2018, please just move on (maybe grumbling at the computer out loud, but don't post it in the comments or put it in a report!).
IF it is on or after 4 April, 2018, AND there is NO other error in your translation, please take a screenshot and post it here. To post a screenshot here, you'll have to upload it to a hosting site like Imgur. Then right click on the picture and click "Copy image address" (or the equivalent in your browser). Then, here, type
!(Pasted image address), replacing "Pasted image address" with what you just copied. Make sure not to leave any spaces.