You can reply to your messages not only from your phone but also from the web.

Notes:

Any SMS replies made from the web will be sent from a YouMail number used to send communications, but it will include the number on your account.
Recipients will not be able to respond to your SMS replies.
Recipients can respond to email replies. Their replies will be sent to the email you have on file with YouMail.

Reply to a message on the web

Sign into your account using the YouMail website.
On the left of the screen, click on Voicemail, then hit Inbox from the dropdown.
Select the message that you would like to reply to, then click the 3 dots located at the top right corner.
Click Reply and select whether you wish to reply by email or text, then enter either the email address or phone number (see Notes).
Type out your message and hit Reply.