#1 Use Voice Control Remote Devices
For each particular smartphone, you own attach it to the specified remote voice speaker and also install the voice assistant apps like Siri, Alexa etc. Make the different commands for the different devices and set up those commands for being accessed for different types of actions. What you have to do is process or speak any command into the remote voice mic and the related device that have that particular command setup would respond. This might require you to spend a lot on the remote mics and speakers but could help you get the support to access different smartphones with just your voice.
#2 Smartphone Hub
Instead of using the numerous apps for a particular kind of purpose try to use the smartphone hub collaborated with the multi-use apps. This could be another way of managing your different smartphones right from the single smartphone. The smartphone hub is the device that connects the different smartphones and let them perform a kind of action collectively.
#3 Use the Tablet for the Purpose
Now what else you can do is use a tablet filled with multiple app sections on the home screen. Connect each of your smartphones with the particular app and then place the app widget on the home screen of the tablet. This could be the best possible option if you could afford the tablet for the very purpose. The best thing is that you can customize and change the home screen anytime on the tablet and hence add or remove the smartphones connected.