To cite coxphw in publications use:

Dunkler D, Ploner M, Schemper M, Heinze G (2018). “Weighted Cox Regression Using the R Package coxphw.” Journal of Statistical Software, 84(2), 1–26. doi: 10.18637/jss.v084.i02.

Corresponding BibTeX entry:

    title = {Weighted Cox Regression Using the {R} Package {coxphw}},
    author = {Daniela Dunkler and Meinhard Ploner and Michael Schemper
      and Georg Heinze},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {84},
    number = {2},
    pages = {1--26},
    doi = {10.18637/jss.v084.i02},