How to secure your Android phone: Switch off Wireless and GPS location (under Location Services) and mobile data (this can be found under Settings > Personal > Location). Note: Only turn on location settings as you need them. It is important to have these services turned off by default as this will reduce the risk of location tracking, save battery power and reduce unwanted data streams initiated by applications running in the background or remotely by your mobile carrier. (Taken from: https://securityinabox.org/en/guide/basic-setup/android)
How to secure your iPhone: Switch off Wireless and GPS location: Settings > Privacy > Location Services and either turn off all Location Services using the Location Services slider or use the individual sliders for each location-aware app or item on your device. To disable Location Services for all websites, turn off Location Services for the Safari app. See How to Turn Off Location Services on iOS|
WhatsApp messages are encrypted (meaning the content of the messages you send can only be seen by you and the recipient) but metadata about who you chat with and for how long is collected and stored.
Signal by Open Whisper Systems is a free and open-source encrypted voice calling and instant messaging application for Android, iOS and desktop. It uses end-to-end encryption to secure all communications to other Signal users. Signal can be used to send and receive encrypted instant messages, group messages, attachments and media messages.