To make your Google groups visible on iPhone, first sync your Google contacts with iCloud/iPhone using the Contacts Sync app.
You can send group emails directly from the Mail app. To do so, open the Mail app, compose an email, and in the "to/cc/bcc" field, type in the first few letters of your group, and the Mail app will prompt you to select your group. Please note that this will only work with the Mail app, and NOT the Gmail app. If you prefer to send group email using the Gmail app, our A2Z Contacts app lets you compose a group email, and then redirect it to the Gmail app.
Unfortunately, the Messages app does not recognize contact groups. However, you can send group messages using A2Z Contacts, a contact management app designed to work well with Contacts Sync. A2Z Contacts can send group messages using iMessages, SMS, and even WhatsApp.
You can download A2Z Contacts from the App Store here:
This help article relates to the iPhone app called "Contacts Sync" which can be downloaded here:
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