Xcode 10 Command PhaseScriptExecution failed with a nonzero exit code (EXPANDED_CODE_SIGN_IDENTITY: unbound variable)

This helped me

sudo gem install cocoapods --pre
pod update

I've read BugReport. Problem was similar to mine and it was fixed in 1.6.0.beta.1 (2018-08-16) (changelog).

Updated(thanks to Cœur)

1.6.0 (2019-02-07) Was published

sudo gem update cocoapods

This should work now.

I have facing the same issue, i believe this issue have something link to keychain access too (code signing problem), I go to keychain access unlock the login then lock it again fixed this issue. After uploading toOSMojave and Xcode 10 keychain need to reverify the password. (how i find this? while facing same issue and trying all available option, i think to generate certificate again, but while generating private key i found keychain login user name and password is wrong type of message- i lock and unlock again solved my problem). Note this process required your login pass phare.

How to fix:- short tip

Go to keychain access -> right click on login -> lock & unlock again 
-> clear Xcode project and make build again.

Some Framework or SDK require Code Signing.

I done code signing and resolved the similar problem for me.