Separating output values with comma

We have a Powershell script which retrieves contents of a Sharepoint list and generates an output, I need to separate multiple values with a Comma.

$aClient = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client")
$aClientRuntime = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime")
$aClientPub = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Publishing.dll")

$username = "xxxxx" 
$password = ConvertTo-SecureString -String 'xxxxx' -AsPlainText -Force
$Url = "https://xxxxxx/sites/"

# SharePoint Online
$ctx = New-Object Microsoft.SharePoint.Client.ClientContext $Url
$ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials $UserName,$Password 

$clientweb = $ctx.Web  
$ctx.Load($clientweb) 
$ctx.ExecuteQuery() 

#Retrieve List
$List = $ctx.Web.Lists.GetByTitle("On Call List")

$qry = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
$items = $List.GetItems($qry)
$ctx.Load($items)
$ctx.ExecuteQuery()

foreach ($item in $items)
{
    $item["Title"]
}

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It produces a result formated like this:
emailaddress1@email.com
emailaddress2@email.com

I need help formatting it as:
emailaddress1@email.com , emailaddress2@email.com