The word aphthartos stresses God’s immortal, un-decaying, or imperishable nature in contrast to men, who do perish and decay. The title “Incorruptible God” uses an older word to express that same nature.
Incorruptible God in Greek:
Ho aphthartos Theos
Strong’s Concordance numbers: 862a, 2316
Bible reference: Rom. 1:23
Professing to be wise, they became fools, and exchanged the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures. (Romans 1:22-23)
The KJV uses the word uncorruptible, while the NIV calls God the immortal God.
In 1 Timothy 1:17, God is called the King eternal, immortal, invisible.