This is the 5208th most frequent Russian word.
номеру
The dative or prepositional case of "номер," meaning "number" or "room."
In this sentence, "номеру" is in the dative case, implying the direction or recipient of the action (the phone number).
Мы отправим сообщение по указанному номеру.
We will send a message to the specified number.
Here, "номеру" is in the dative case, referring to the hotel room number, suggesting a location.
Она живёт в следующем номере гостиницы.
She lives in the next room of the hotel.
"Номеру" in this sentence is used in the context of identification (license plate number), denoting an attribute of the cars.