Adding a reserved public IP on the classic Azure portal

#Connect to Azure
Add-AzureAccount

#Select Subscription
get-azuresubscription | out-gridview -passthru | select-azuresubscription

#Check for Reserved IP
Get-AzureReservedIP

#Reserve the current IP
New-AzureReservedIP –ReservedIPName MyReservedIP –Location "UK South" -ServiceName MyCloudService

#Check for Reserved IP
Get-AzureReservedIP

More details @ https://docs.microsoft.com/en-us/azure/virtual-network/virtual-networks-reserved-public-ip