'phone volume' is correct and can be used in written English.
It refers to the loudness of the sound coming from a phone when an incoming call is being received or when a person is speaking on the phone. For example, "She had to turn up the phone volume to hear her friend's voice clearly."
During the quarter ending Sept. 30, "mobile phone volume growth for Nokia and the industry over all has been strong," the company said.
"In the near term, we plan to drive Windows Phone volume by targeting the more affordable smartphone segments, which are the fastest-growing segments of the market, with Lumia.
However since 2015 customer service phone volumes have dropped 17%.
"It is therefore important for Nokia to continue leading the Windows Phone volumes.
Meanwhile, feature phone volumes grew by two percent to 73.5 billion units.
We can compile phone book sized volumes of regulations and best practices, but if they are too cumbersome to be read then they are useless.
Mobile Phones ASP represents Mobile Phones net sales divided by Mobile Phones volumes.
"Nokia has the mobile-phone volumes, but Apple has proven that they have a strong user acceptance for applications".
The sequential decline in our Mobile Phones volumes in the first quarter 2012 was most pronounced in India and Europe, primarily due to the factors mentioned above.
The sequential decline in our total Devices & Services volumes in the first quarter 2012 was driven by significantly lower Mobile Phones volumes and Smart Device volumes, including lower seasonal demand for our devices, as discussed below.
Volume On a year-on-year basis, the decline in our Mobile Phones volumes in the first quarter 2012 was primarily driven by our reduced portfolio of higher priced feature phones compared to the first quarter 2011, partially offset by sales of recently introduced products which represented a higher proportion of our portfolio.
