Answer by taking a quote from the following article:

Phineas P. Gage (1823-1860) was an American railroad construction foreman remembered for his improbable[B1]:19 survival of an accident in which a large iron rod was driven completely through his head, destroying much of his brain's left frontal lobe, and for that injury's reported effects on his personality and behavior over the remaining 12 years of his life--effects sufficiently profound (for a time at least) that friends saw him as "no longer Gage". [H]:14 Long known as the "American Crowbar Case"--once termed "the case which more than all others is calculated to excite our wonder, impair the value of prognosis, and even to subvert our physiological doctrines" --Phineas Gage influenced 19th-century discussion about the mind and brain, particularly debate on cerebral localization,  [M]:ch7-9[B] and was perhaps the first case to suggest the brain's role in determining personality, and that damage to specific parts of the brain might induce specific personality changes.  [M]:1,378[M2]:C  :1347  :56

Macmillan's analysis of scientific and popular accounts of Gage found that they almost always distort and exaggerate his behavioral changes well beyond anything described by anyone who had direct contact with him, concluding that the known facts are "inconsistent with the common view of Gage as a boastful, brawling, foul-mouthed, dishonest useless drifter, unable to hold down a job, who died penniless in an institution".  In the words of Barker, "As years passed, the case took on a life of its own, accruing novel additions to Gage's story without any factual basis".[B]:678 Even today (writes Zbigniew Kotowicz) "Most commentators still rely on hearsay and accept what others have said about Gage, namely, that after the accident he became a psychopath";[K2]:125 Grafman has written that "the details of [Gage's] social cognitive impairment have occasionally been inferred or even embellished to suit the enthusiasm of the story teller";[G]:295 and Goldenberg calls Gage "a (nearly) blank sheet upon which authors can write stories which illustrate their theories and entertain the public".  For example, Harlow's statement that Gage "continued to work in various places; could not do much, changing often, and always finding something that did not suit him in every place he tried" [H]:15 refers only to Gage's final months, after convulsions had set in.[M]:107[M10]:646 But it has been misinterpreted as meaning that, after his accident, Gage never held a regular job, "was prone to quit in a capricious fit or be let go because of poor discipline",:8-9 "never returned to a fully independent existence",:1102 "spent the rest of his life living miserably off the charity of others and traveling around the country as a sideshow freak", and ("dependent on his family"  or "in the custody of his parents") died "in careless dissipation". In fact, after his initial post-recovery months spent traveling and exhibiting, Gage supported himself--at a total of two jobs--from early 1851 until just before his death in 1860.  [M10]:654-5[D]:77  Other behaviors ascribed to the post-accident Gage that are either unsupported by, or in contradiction to, the known facts include:  None of these behaviors is mentioned by anyone who had met Gage or even his family, and as Kotowicz put it, "Harlow does not report a single act that Gage should have been ashamed of." [K2]:122-3 Gage is "a great story for illustrating the need to go back to original sources", writes Macmillan, most authors having been "content to summarize or paraphrase accounts that are already seriously in error". [M]:315  Nonetheless (write Daffner and Searl) "the telling of [Gage's] story has increased interest in understanding the enigmatic role that the frontal lobes play in behavior and personality", and Ratiu has said that in teaching about the frontal lobes, an anecdote about Gage is like an "ace [up] your sleeve. It's just like whenever you talk about the French Revolution you talk about the guillotine, because it's so cool." [K] Benderly suggests that instructors use the Gage case to illustrate the importance of critical thinking.

In what other ways was the mental change exaggerated?
"inconsistent with the common view of Gage as a boastful, brawling, foul-mouthed, dishonest useless drifter, unable to hold down a job, who died penniless in an institution".