Here's some of my configuration's settings, try putting them in yours (dosboxPHANT.conf) and see how it works out:

[sdl]
fullscreen=true
fulldouble=true
fullresolution=1920x1080 (your res)
windowresolution=original
output=openglnb
autolock=true
sensitivity=100
waitonerror=true
priority=higher,normal
mapperfile=mapper-0.74.map
usescancodes=true

[dosbox]
language=
machine=svga_s3
captures=capture
memsize=16

[render]
frameskip=0
aspect=true
scaler=none

[cpu]
core=auto
cputype=auto
cycles=auto
cycleup=10
cycledown=20

[mixer]
nosound=false
rate=44100
blocksize=1024
prebuffer=50

[midi]
mpu401=intelligent
mididevice=default
midiconfig=

[sblaster]
sbtype=sb16
sbbase=220
irq=7
dma=1
hdma=5
sbmixer=true
oplmode=auto
oplemu=default
oplrate=44100