Below are the instructions for voicemail retrieval for your Vtech CS5121-2 5.8 GHz Twin 1-Line Cordless Phone. I have included an easily clickable and printable PDF link of the user's manual for this phone from the official vtech web site.
I hope this helps you!
New message indication
The message display counter will flash when there are new answering system messages.
If the new message alert tone is turned on, the telephone base will beep every ten seconds when there are unreviewed messages.
Press /PLAY/STOP to listen to messages.
Press /PLAY/STOP again to stop playback.
If you have new messages waiting, you will hear only new messages (oldest first). If there are no new messages, the system will play back all messages (oldest first).
When playback begins, the total number of messages is announced, followed by the day and time of the first message to be played.
Options during playback
Press VOL+/VOL to adjust the speaker volume.
Press >>/SKIP to skip to the next message.
Press<</REPEAT to repeat the message currently playing.
Press <</REPEAT twice to listen to the previous message.
Press X/DELETE to delete the current message. The system will advance to the next message.
Click below for PDF USER'S MANUAL