All his calls are "perfect"

Since taking office, Trump has been cautioned against unsecured lines multiple times. But he has continued to call people on a number he held since before his time in the White House, including making calls from that number in the last several weeks, people familiar with those calls say. He also has a second number he uses, which is government-issued.

 [...]

CNN stands by its reporting.

These are cell phones Trump has personally been issued. They are considered to be less secure than landline White House phones presidents typically use, and he has been cautioned against using them to make secure calls, sources tell CNN.

CNN previously reported that Trump has given his personal number to foreign leaders on multiple occasions, outright ignoring security protocols. According to The Washington Post, Trump handing out his personal line led to one-on-one calls that even top White House aides did not know about.

[...]

The New York Times reported last year that Chinese and Russian spies have listened in on Trump's calls on his personal cell phone and the President's aides have told him that Russian spies were listening in on a regular basis.

  CNN

He's counting on it.

For a brief period earlier in his term, Trump agreed to stop using his personal device, but quit after he realized all of his calls could then be monitored on a call log list.

I don't know if it's more naive or ignorant that he didn't realize that from the outset.

Among the privileges and cool stuff that come with being the president of the United States is a highly modified Boeing Black smartphone, an encrypted device certified to handle Top Secret data. The Defense Department Information Systems Agency, or DISA, developed the phone with help from Boeing and other partners, the phone “goes with the office” of the President. But is Donald Trump using it — or his old and far less secure Android phone?

[...]

As of November 1, DISA had handed out at least two of the phones, to President Obama and to Cyber Command leader Adm. Mike Rogers, according to DISA chief Lt. Gen. Alan Lynn, who spoke at the Milcom conference in Baltimore.

[...]

When we asked whether Obama’s Boeing Black phone had been given to Donald Trump, a DISA official, speaking on background, said only that the phone “goes with the office of that position.”

  Defense One (2017)

If Obama used it, that would certainly be a factor why Trump doesn't.

The phone’s most important and famous feature: when you try to break it open, it self-destructs. According to the FCC filing: “Any attempt to break open the casing of the device would trigger functions that would delete the data and software contained within the device and make the device inoperable.”

Boeing would not discuss how the phone has changed since those 2014 filings.

Almost no data resides on the phone itself, which [was] described as being “close to a VDI,” a virtual desktop infrastructure. That means that the phone is little more than a window into another computer somewhere else. In addition, there is “a large amount of encryption tied into it.”

And creates a call record.

...but hey, do what you want...you will anyway.