Patrick Lovato - who has been estranged from his Disney star daughter for over two years - spoke with her from the facility she was admitted to at the beginning of this month to deal with "emotional and physical issues".
He told website RadarOnline.com: "Demi`s doing great, she`s such a strong girl."
Patrick also revealed he and the 18-year-old singer-and-actress discussed his present cancer battle and he said he is positive she is on the road to recovery.
He added: "She told me she loved me, she really loves her daddy. She told me she`s getting better."
Patrick is hopeful that Demi`s good progress in rehab could lead to a full reconciliation once she leaves the unnamed facility.
He said: "All I`ve got here is my dog Daytona but I`ve offered to let Demi come and stay here any time she wants to."
It has been claimed that one of the reasons behind the teenager`s problems was the shock death of her secret boyfriend earlier this year.
Demi reportedly struck up a romance with David Osborn after meeting him at a house party last December, and was left heartbroken when the 21-year-old Texan musician died in an accident when riding on a rubber tube down the Brazos River in July.
Speaking about the tragedy, Patrick said: "She was really heartbroken. She was really in love with the guy.
"Bless her heart. She`s always been an honest person, what can I say?"
Demi - who is also Texan - paid tribute on her twitter page at the time, writing: "Can`t wait to see you again in heaven... Texas isn`t the same without you... RIP Dave Osborn."