Why does my cell phone get less efficient with each update, regardless of the fact that I do not install apps, and I clean off the old data regularly? Are the phone manufacturers engaged in planned obsolescence, or is it the service providers?
There could be several reasons why your cell phone gets less efficient with each update.

Firstly, updates often come with new features that require more processing power and memory, which can slow down older devices.

Secondly, updates may not be optimized for older devices, leading to performance issues.

Thirdly, app developers may update their apps to work with newer operating systems, which may cause compatibility issues with older devices.

While it is true that some manufacturers and service providers engage in planned obsolescence, it is difficult to determine if that is the case in your specific situation. However, it is generally recommended to upgrade your device every few years to keep up with advancements in technology and ensure optimal performance.
What can I do to improve my phone's performance after it has updated?
This can vary depending on the exact phone that you have. To help me get a general idea, are you trying to speed up an iPhone, an Android phone, or something different?