In order to display a conference room’s calendar on a mobile device, there are usually two options: use an Office365 account with delegate rights to open a room’s mailbox or to enable the AD user account for that particular room mailbox.
The first solution is the simplest, however has the following limitations: requires a mobile app capable to differentiate between the Office365 account and the mailbox, and uses up one Exchange license. The second solution is even simpler, works with any mail/calendar mobile app that can connect to Office365 and does not use an Exchange license:
Start a remote Powershell session with Exchange Online, entering a tenant admin’s credentials:
$credential = Get-Credential
$session = New-PSSession -ConfigurationName Microsoft.Exchanged -ConectionUri https://outlook.office365.com/powershell-liveid/ -Credential $credential -Authentication Basic -AllowRedirection
$passwd = ConvertTo-SecureString -String <room mb password> -AsPlainText -Force
Set-Mailbox -Identity “<room mb address>” -EnableRoomMailboxAccount $true -RoomMailboxPassword $passwd