Here’s my take on this.
I can see both sides of the argument here. On one hand, a sudden increase in phone secrecy is a classic red flag for many people. Habits like clearing chats, changing passwords, or never leaving the phone unattended can certainly point to something being hidden. It’s understandable why that would create a sense of unease.
On the other hand, such behavior isn’t always proof of cheating. It could be related to work stress, planning a surprise, or a number of other private matters.
If direct conversation isn’t providing the clarity you need, using a monitoring tool to see WhatsApp activity can be a way to get a definitive answer. It can help you understand the full context of the communications, which can either confirm your suspicions or hopefully put your mind at ease.