iPad Safari link: How to share it to Google Voice SMS Message
Normally what you would do is, with the web page/url you want to share in Safari, is to tap the share button and if the App is not listed scroll to the right and tap the "..." menu and add the Voice.app to the list.

From what I can see on my iPhone (iOS 12.4.1, latest G Voice) Google has not exposed the Voice app so that this can be done. There seems to be no options to add Voice to the share sheet, nor is there anything in Voice settings to activate that functionality.

Your only available method seems to be to just copy the link and then paste it into the Messages.app. At least until Google decides to change Voice to allow for it as a target for sharing.