So far the only way that I have been able to achieve this is utilizing the 365 plugin on my web browser through Chrome. But my preference is to use the Outlook app want to be able to dial numbers from my Outlook contacts.
Ringcentral's marketing materials make it appear that the entire MS 365 suite is fully integrated but does not make it clear this is only for Windows operating systems until you dig deeper into the downloadable spec sheets. Our firm is entirely on MACs. The lack of iOS compatibility really limits the functionality of your products.