Translation:Is this the engineer's phone number?
How what indicates "the engineers phone number" vs "Is this phone number the engineer's?"
I didn't understand your question clearly, but maybe you are asking how the Arabic sentence means "is this ...etc" ?
If this is the case, in Arabic, to ask questions that usually start with "is" or "does" in English (or yes/no questions), Arabic has special articles for that, which is هل (hal).
This is the engineer's phone number: هذا رقم هاتف المهندس (háðá raqmu hátif-il-muhandis).
Is this the engineer's phone number?: هل هذا رقم هاتف المهندس (hal háðá ramu hatif-il-muhandis).
Hope this answers your question.
The way I'm reading your question, you're asking for the difference between the phrases "Is this the engineer's phone number" and "Is this phone number the engineer's." Since these both have the same sentiment, it's possible they're translated the same. I don't know for sure though, so maybe a native speaker will elaborate.