You can always give a suggestion of what Bamber said. He never has although must remember.
So if he planned this meticulously down to false phone calls , leaving a staged suicide , leaving no forensic link to himself , getting rid of his clothes, etc etc then why would he admit a call that he can't remember?
In retrospect did he feel stupid and selfish for not taking his fathers call more seriously and taking more notice of what he said and doing the right thing ? Rather than hesitating , not calling 999 , or calling someone else to help? Did he feel that by panicking and ringing Julie for some sort of reassurance and advice he had done his father a misjustice , let him down when he needed him most ?
Sounds more likely than a chink in the armour of his perfect plan .