WhatsApp has been planning on adding a new Companion mode for you to link two smartphones to one WhatsApp account for a while now. Recently, this feature became available for Android tablets and as part of a beta update and now, the same is being tested for a secondary smartphone.
A recent report by WABetaInfo reveals that WhatsApp has started rolling out the Companion mode for some Android users as part of beta version 2.22.24.18. This will let you link a secondary phone to the same account so that managing it on two devices becomes easier.
Once two mobile phones are linked by following the on-screen instructions, all your chats will be synced to the secondary phone. However, some features will remain unavailable due to the beta nature of the feature These will be the ability to view live locations and manage broadcast lists and stickers. The chats and calls will be end-to-end encrypted.