So far you probably had a generic voicemail greeting on your iPhone and want to change it to a personal voicemail greeting and with most carriers you don’t even need an additional voicemail recording app and can record a custom voicemail greeting directly on iPhone.
Android phones can access voicemail by holding down the 1 key on the dial pad until the phone dials your 10-digit phone number. You will automatically connect to your mailbox and be prompted to enter your temporary password; this password is the last 4 digits of your phone number followed by the # key. Start the Google Voice app. Tap the three horizontal lines at the top left of the screen (sometimes called a hamburger menu), and then tap “Settings.” In the Voicemail section, tap “Voicemail greeting.” Tap “Record a greeting.” How do I access my voicemail? To call your voicemail on an Android phone, simply open your phone’s dial pad and hold your finger down on the “1” key. You can also call your voicemail from a different phone by calling your own number and tapping the pound key. How do you check your voicemail?

Standard greeting with your name: "At the tone, please record your message to [name]."
In your Phone app, navigate to the number pad. Pressing and holding the 1 key will dial you into your Voicemail's main menu instantly. You can also call your own number or select Voicemail from the list of options under the three-dot menu in the app. If this is your first foray into the matter, the friendly voice on the other end will guide you