How to implement CODED_PHY in ble_app_uart in SDK 15.3.0

I am working long nrf52840 and trying to implement long range in my project. There were examples in SDK 15.2.0 but i couldn't find any example or post which is related to SDK 15.3.0. I tried my own modification like changing the advertising layer from 1 Mbps to CODED in ble_adverstisement.c file(15.3.0) but after i made the changes my device keep resetting. I did not make any other changes in sdk_config and main. file

p_advertising->adv_params.secondary_phy   = BLE_GAP_PHY_CODED;
this line i added in ble_advertisement_init() function. i don't more what changes need to be done to make it work in coded mode.